Field of the Invention
This invention relates to an anti-skid brake control system for motor vehicles and more particularly to an anti-skid actuator including a power diaphragm movable piston in a housing to effect movement of a pressure modulating piston in response to a pressure differential thereacross.
Description of the Prior Art
In the known type of the actuators, the power piston ordinarily has a sliding fit on a guiding member stationary in the housing, so that the piston may flutteringly reciprocate on the guide member in order to effect movement of the pressure modulating piston or plunger for anti-skid purposes. The power piston has a blind bore in the central portion and the guide member projects from the internal face of the housing for a sliding fit engagement with the bore of the power piston.
This prior art arrangement, however, tends to render the actuators inoperative due to loss of the lubricant grease from out of the blind bore over a period of time caused by the fluttering reciprocation of the piston. The deficiency further tends to result in an insufficient lubrication of the piston on the guiding member and hence to an abrasion of the guide member and blind bore assembly. The resultant powdered metal caused by the insufficient lubrication is considered as a great disadvantage and short-coming in practice, in that it would tend to offer other deficiencies in the closed and non-accessible interior of the housing. The arrangement has further proven to offer another deficiency in practice, in that a cavity defined between the end face of the guiding member and the bottom of the blind bore varies in volume synchronously with the reciprocation of the power piston thus causing alternately vacuum and compressed pressures in the cavity and thence a resistance against the reciprocation of the power piston on the guiding member.